An AlGaAs surface-emitting semiconductor laser device extracting laser light from a direction perpendicular to a substrate surface has semiconductor multilayer film reflectors in a vertical direction of an active layer, in order to make up an optical resonator. The semiconductor multilayer film reflector is configured of first and second semiconductor layers which are stacked alternately and have respective bandgap energies larger than energy corresponding to an oscillation wavelength of laser light.
In the semiconductor multilayer film reflector, the first and second semiconductor layers having a large refractive index difference, namely, a large bandgap energy difference therebetween are selected in order to realize a high reflectance. This results in a higher heterojunction barrier produced on a junction of the layers. Consequently, there arises a problem that this prevents electrons or hole current from flowing, with the result that the semiconductor multilayer film reflector has a high resistance value. Undermentioned Patent Document 1 discloses a technique to realize resistance reduction of the semiconductor multilayer film reflector by interposing a non-doped third semiconductor layer between the first and second semiconductor layers thereby to lower a hetero barrier of the heterojunction of the first and third semiconductor layers. The third semiconductor layer has the same composition as the second semiconductor layer and a smaller layer thickness than the second semiconductor layer. As a result, the tunneling of electrons or hole is enhanced.